System for controlling the entry and exit of workpieces into and from a heating furnace



March 24, 1970 w, 300 3,502,234

SYSTEM, FOR CONTROLLING THE ENTRY AND EXIT OF WORKPIECES INTO AND FROM AHEATING FURNACE Filed June 7, 1968 4 Sheets-Sheet 1 fi A e 1 3 k a March24, 1970 w, coo 3,502,234

SYSTEM FOR CONTROLLING THE ENTRY AND EXIT OF WORKPIECES INTO AND FROM AHEATING FURNACE FIG.4.

WITNESSES INVENTOR W 2 John W. Cook March 24, 1970 J. w. cooK 3,502,234

SYSTEM FOR CONTROLLING THE ENTRY AND EXIT OF WORKPIECES INTO AND FROM AHEATING FURNACE Filed June 7, 1968 4 Sheets-Sheet 5 United States PatentU.S. Cl. 21426 11 Claims ABSTRACT OF THE DISCLOSURE This inventionrelates to a control system for controlling the delivery and dischargeof workpieces or slabs into and from a furnace operative with a hotstrip rolling mill. A computer may be utilized to control a pusherassembly to serially deliver one or more of the slabs from a furnacecharging table onto the skids that run the length of the furnace. At theexit side of the furnace, the computer controls an extractor assembly toenter the furnace and to extract each slab to be delivered and to placeit onto a delivery table. The slabs are disposed within the furnace inan abutting relationship so that as a slab is pushed from the furnacecharging table and against the first slab in the series of slabs Withinthe furnace, then the last slab in the furnace is pushed into a position'where the extractor may withdraw it from the furnace. The computer hasa capability for storing the dimensions of each individual slab andserves to control the distance the series of slabs are pushed to ensurethat the last slab in the furnace is disposed in a position so that theextractor may readily take it from the furnace.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a system for controlling the positioning of a plurality ofworkpieces or slabs, and more particularly to a system for controllingthe entry and exit of each of a plurality of slabs to and from a furnaceoperative with a hot strip rolling mill.

Description of the prior art In a typical hot strip steel mill,workpieces or slabs, which have been previously rolled from ingots ordirectly cast, are taken to the hot strip mill where they are convertedthrough rolling from slabs to coils of steel strip. Typically, slabs aretaken to the hot strip steel mill in piles where they are sorted andeach arranged to be sent through a heating furnace in preparation tobeing rolled into a long strip. The slabs are taken from the furnace andare directed first through a roughing mill which may consist of aplurality of stands to successively reduce the thickness of the slab,and then through a finishing mill which further reduces the thickness ofthe elongated slab into a desired thickness. After passing through thefinishing mill, the strip is then wound upon a coiler and taken from themill.

More specifically, a pile of slabs may be taken to the mill where theslabs are deposited upon a receiving table. Next the pile of slabs istaken to a depiler assembly where the topmost slab is removed and theslabs placed one at a time onto the first furnace receiving table. Aplurality of serially oriented furnace charging tables are provided totake the slabs individually from the depiler assembly and to positionthem so that they may be pushed into one of a plurality of furnaces. Asuitable control system may be provided for accurately positioning eachof the slabs upon a furnace charging table. The slabs come in a varietyof ranges of length and are carefully 3,502,234 Patented Mar. 24, 1970positioned in accordance with their respective lengths before they areplaced in the furnace. A control system and a plurality of detectors canbe provided so that the slabs may be disposed evenly within the furnace.The furnaces include a plurality of burners disposed evenly throughoutthe furnace and may heat each of the slabs to a temperature ofapproximately 2350" F. The heating process may require several hours toevenly heat each of the slabs throughout its thickness. The slabs arethen taken from the furnace and are disposed in the finishing androughing mills in order to reduce the thickness of the slabs and to formstrips which are eventually coiled as explained above.

It has been typical of the prior art practice for the operator to effectthe desired placement of the slabs into and from the furnace by manualcontrol. It is normally not convenient to place the operator in aproximate position to the furnace charging tables or the furnacedelivery tables such that the operator must normally view the placementof the slabs by means of television monitors. Illustratively, the slabswould be removed from the furnace by sliding the slabs downward from thefurnace skids onto the delivery tables. The furnace delivery tableswould be provided with bumpers to stop the slabs. Typically, theoperator would view the placement of the slabs to be removed upon atelevision monitor and manually control a pusher to slide the entire rowof slabs until the last slab slides onto the furnace delivery table.More recently, extractor assemblies have been developed for withdrawingslabs from furnaces. Typically, extractor assemblies serve to lift theslabs from the skids of the furnace and to place them on a furnacedelivery table. The operation of the extractor assembly has beenperformed manually by an operator, who visually checks the movement ofthe extractor. It is particularly pointed out that such operations aretime consuming and require much of the operators time and attention.

It is therefore an object of this invention to provide a new andimproved system for better controlling the delivery to and exit of slabsor workpieces from a furnace.

SUMMARY OF THE INVENTION This and other objects are accomplished inaccordance with the teachings of this invention by providing a new andimproved slab control system including a pusher assembly for deliveringa plurality of slabs one at a time into a furnace, an extractor assemblyfor removing a plurality of said slabs one at a time from the furnaceand depositing them on a furnace delivery table from which they are sentto the roughing mill. The system of this invention may include acomputer having the capability for storing the dimensions of each of theplurality of slabs and for controlling the stroke of the pusher relativeto each slab so that the series of abutting slabs within the furnace aremoved a distance corresponding to a width of the last slab. As a result,the last slab is disposed in an extracting position from which theextractor assembly, when desired, removes the slab from the furnace. Thecomputer may also serve to control the placement of the slab to beremoved by the extractor to position correctly the slab on the furnacedelivery table.

DESCRIPTION OF THE DRAWINGS These and other objects and advantages ofthe present invention will become more apparent when considered in viewof the following more detailed description and drawings, in which:

FIGURE 1 is a side view of a furnace delivery and exit system inaccordance with the teachings of this invention;

FIG. 2 is a plan view of a furnace charging table and pusher assemblywhich may be incorporated within the system of FIG. 1;

FIG. 3 is a plan view of a furnace delivery table and an extractorassembly which may be incorporated within the system of FIG. 1;

FIG. 4 is a view of the assembly for lifting the extractor doors and thefurnace exit doors for respectively allowing the extractors to enter andto extract slabs from the furnace of FIG. 1; and

FIG. 5 is a schematic diagram of a computerized control system forregulating the pusher assembly and the extractor assembly as shown inFIG. 1 in accordance with the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,and in particular to FIG. 1, there is shown an illustrative embodimentof a furnace delivery and extracting system in accordance with theteachings of this invention. A plurality of slabs 40 are brought one ata time to a furnace charging table 12 and are positioned thereon so asto evenly charge a furnace 32. Then the slabs 40 are pushed from thefurnace charging table 12 onto a plurality of skids 36 which run thelength of the furnace 32. As shown in FIG. 1, the slabs 40 within thefurnace 32 are disposed in an abutting relationship with the front edgeof the leading slab 40a coinciding with an index line 44. As will beexplained in greater detail later, a pusher assembly or displacementmeans 18 slides a slab 40 from the furnace charging table 12 onto theskids 36 to abut the trailing edge of the last slab 4012 within thefurnace 32. The pusher assembly 18 slides the entire line of slabs 40 adistance corresponding to the width W of the leading slab 40a so thatthe leading slab 40a is then disposed in an extracting position 45 readyto be taken by an extractor assembly or displacement means 60 from thefurnace 32 and deposited centrally upon a furnace delivery table 50. Itmay be understood that there may be a plurality of furnaces similar tofurnace 32 disposed in parallel between a plurality of furnace chargingtables and a plurality of furnace delivery tables. The furnace deliverytables transport the slabs 40 into the roughing and finishing millswhere the thickness of the slabs is successively reduced.

A slab will be brought as explained above, from the depiler assembly tothe furnace charging table preceding the furnace charging table 12 shownin FIGS. 1 and 2, where the slab 40 is held until it may be charged infurnace 32. The slab 40 upon command will be brought from the precedingcharging table onto the furnace charging table 12 which includes aplurality of rollers 14 driven through a suitable gearing by a suitabledrive motor (not shown). If the furnace 32 is in need of additionalslabs, the slab 40 will be brought to its correct position with regardto the plurality of skids 36.

Once the slab 40 is correctly disposed upon the furnace charging table12, the pusher assembly 18 is activated to slide the slab 40 from thefurnace charging table 12 onto the skids 36. The pusher assembly 18includes a pair of pushers 20, which are supported upon a plurality ofrollers 28 to be driven in a reciprocal, rectilinear motion. Each of thepushers 20 includes a rack 21 whose teeth mesh with a pinion gear 30.The pinion gears 30 are connected to a drive shaft 22 (as shown in FIG.2) which is driven by a pair of motors 24. As shown in FIGS. 1 and 2each of the pushers 20 have a head assembly 25 from which are suspendeda plurality of teeth 26 by pins 27. When the pushers 20 are drivenforward, the teeth 26 will abut against the slab 40 to slide the slab 40onto the skids 36. It is noted that the teeth 26 are suspended upon thepins 27 to allow the teeth to rotate counterclockwise as shown in FIG. 1if they strike an object such as another slab upon their retractingcycle. As shown in FIG. 2, a suitable speed indicator 38 such as atachometer is connected to the motors 24, and further, suitable positionsensors 39 such as selsyn transmitters are connected to the drive shaft22 to provide an output signal accurately indicating the position of thepushers 20. In addition, limit switches 41 are connected to the shaft 22to generate an electrical signal indicating when the pushers 20 aredisposed in their retracted position.

A slab 40 is slid from the furnace charging table 12 onto the skids 36so that the leading edge of the slab 40 abuts the trailing edge of theslab 4011 whose leading edge is disposed within the furnace 32. As shownin FIG. 1, the furnace 32 has an entrance door 34 which is disposed inan open position to allow the slabs 40 to be slid therethrough. In orderto help explain the operation of this system, the slabs 40 have beendesignated with sufiixes to designate their position within the furnace32. More particularly, the slab 40a has its leading edge disposed uponthe index line 44. Slab 40 is that slab being pushed from the furnacecharging table 12 onto the skids 36, and slab 4011 is that slab with itsleading edge within the furnace 32 and against which the slab 40,, is tobe pushed. As shown in FIG. 1, the leading edges of the slabs 40 abutthe trailing edge of the next slab 40 so that if slab 4011 is pushed thefollowing slabs will be pushed forward so that slab 40a will be disposedin the extracting position 45.

As the slab 40a is being disposed in the extracting position 45, thesets of furnace exit doors 46 and extractor doors 48 are lifted upwards,and the extractor assembly 60 is activated to move to the left as shownin FIG. 1, to extract the slab 40a, and to deposit it centrally upon thefurnace delivery table 50. As shown in FIGS. 1 and 3, the furnacedelivery table 50 includes a plurality of rollers 52 and a table motor58 for driving through a reducer 56 and appropriate gearing 54, therollers 52. The extractor assembly 60 includes a plurality of extractors62, which as shown in FIG. 3, extend between the rollers 52 of thefurnace delivery table 50, and which are driven into the furnace 32through the doors 48 by a pair of traverse motors 92. Normally, thetraverse motors 92 are interconnected through shafts 97 and a magneticclutch 95. However, when it becomes necessary to extract a pair ofdouble row slabs 40, one of the motors 92 may be energized to insert oneof the extractors 62 to withdraw one of the pair of slabs, and then theother traverse motor 92 may be energized to remove the other slab 40.

As shown more clearly in FIG. 1, each of the extractors 62 includes adrive extension 64 to which is secured a rack 66. The teeth of the rack66 mesh with the teeth of a pinion gear 68. The pinion gears 68 are inturn driven by a drive shaft 69. As shown in FIG. 3, the drive shaft 69is connected to the motors 92 by reducer gearings 94. When the traversemotors 92 are energized, the drive shaft 69 will be driven to displacethe extractors 62 in a substantially rectilinear motion. Each extractor62 includes an extractor finger 70 which may be driven to the right asshown in FIG. 1 between the rollers 52 and into the furnace 32. Suitablerollers 71 and 73 are provided for directing and confining therectilinear motion of the drive extensions 64 along a substantiallylinear path, Further, suitable sets of wheels 72 are rotatably connectedto each of the extractors 62 to allow the extractors 62 to be rolledforward upon a lift assembly 74. As shown more clearly in FIG. 3,suitable speed detectors 96 such as tachometers are connected to each ofthe traverse motors 92, and suitable positioning detectors 98 such asselsyn transmitters are connected to the traverse motors 92 to provideelectrical signals indicative of the position of the extractors 62.Further, the drive shafts 69 are connected to limit switches 75, whichgenerate signals indicative of when the extractors 62 are in their fullyextended position.

As seen more clearly in FIG. 1, the traverse motors 92 drive theextractor 62 in a rectilinear motion forward into the furnace 32 uponthe wheels 72. The wheels 72 roll upon the lift assembly 74 which may beraised and lowered by a pair of lift motors 88. As shown in FIG. 3,

the lift motors 88 are interconnected by shafts 81 to a magnetic clutch83. The magnetic clutch 83 allows the lift motors 88 to be operatedseparately to extract one of a pair of slabs from the furnace 32.Further, the lift motors 88 are connected to gearing mechanisms 78,which drive rotating members 80. As shown in FIG. 1, the lift assembly74 includes a lift platform 76, which is pivotally connected to a pairof idler arms 82 and 84. The other ends of the idler arms 82 and 84 arealso pivotally connected to a support or base member. A connecting rod86 is eccentrically attached at one end to the member 80 by a suitablepin and fastened at the other end pivotally to the lift platform 76.When the connecting rod 86 is driven forward by the member 80, the liftplatform 76 is pushed to the left as shown in FIG. 1, and the idler arms82 and 84 are rotated counterclockwise (as shown in FIG. 1) to therebylift the platform 76 upward. When the lift platform 76 is in its firstor down position, the extractors 62 may be driven forward and into thefurnace 32 without interfering with the slabs to be disposed upon thefurnace delivery table 50. More specifically, as shown in FIG. 1, theheight of the extractor fingers 70 is below the upper surface of therollers 52 of the furnace delivery table 50. As shown in FIG. 3,suitable limit switches 90 are connected to the lift motors 88 toprovide an electrical signal indicating when the lift platform 76 is ina second or up position. Further, a suitable interlock mechanism may beconnected to the limit switches 90 to prevent the table motor 58 fromdriving the rollers 52 of the furnace delivery table 50 when the liftplatform 76 is in up position.

Referring now to FIG. 4, a door motor 100 is provided for raising theextractor doors 48 and the exit doors 46 to allow the extractors 62 toenter the furnace 32 and to withdraw the slab 40a. More specifically,the door motor 100 is connected through a reducer gearing 102 to a driveshaft 104. Pluralities of wheels 110 and 111 are fixedly secured to thedrive shaft 104 for respectively raising and lowering the extractordoors 48 and the furnace exit doors 46. Suitble flexible linkages 108and 109 are respectively interconnected between the doors 48 and thewheels 110, and the doors 46 and the wheels 111. In addition, a suitablelimit switch 106 is connected to the drive shaft 104 to provide anindication of when the doors 46 and 48 are opened or closed.

Referring now to FIG. 5, there is shown a control system 112 fordelivering and extracting a plurality of slabs 40 into and from thefurnace 32. The control system illustratively includes a computer 114which in one embodiment serves to control the stroke of the pushers toplace the slab a in the extracting position and also to control thewithdrawal stroke of the extractor assembly to precisely position theslab 40a upon the furnace delivery table 50. The dimensions and othercharacteristics of the slabs 40 are fed into the computer 114 by aninput card reader 118. Typically, a card with the dimension data of aslab 40 is placed in the order of its processing into the card reader118, which transfers this information into a storage facility within thecomputer 114.

The computer 114 functions to supply data corresponding to the widths ofslabs 40 to the various position controls associated with the pusherassembly 18 or the extractor assembly 60. As discussed with reference toFIG. 2, a pair of pushers 20 are driven by the motors 24 through thedrive shafts 22, which are connected to the position sensors 39.Further, the speed detectors 38 are connected mechanically to the pushermotors 24. An output signal indicative of the speed of the motors 24 isdeveloped by the speed detectors 38 and is applied to a pusher regulator124. In a similar manner, a signal indicative of the position of thepushers 20 is applied by the position sensor 39 to a position controlcircuit 116. As will be explained later, the computer 114 may initiatethe operation of the pusher motors 24 and the control stroke throughwhich the motors 24 drive the pushers 20. The position control 116 inturn applies a signal to the pusher regulator 124 indicative of thedesired stroke or movement of the pusher 20. The pusher regulator 124determines the speed of the pusher motors 24 by regulating the potentialsupplied by a power supply 126 to the pusher motors 24. The output ofthe speed detector 38 is applied to the pusher regulator 124 to completea feedback control loop to ensure that the pushers 20 are being drivenat the correct speed. In addition, a manual control may be connected tothe pusher regulator 124 whereby an operator may override the commandsof the computer 114 and control manually the speed of the pushers 20. Inaddition, a manual initiate control 122 may be applied to the positioncontrol 116 to allow the operator to manually control the position ofthe pushers 20. As will be explained in detail later, the pushers 20 maybe operated in a semi-automatic mode, wherein the operator may apply anappropriate signal developed by a semi-auto control 120 into theposition control 116 to control the stroke of the pushers 20.Illustratively, the semi-auto control may include a decade switch tosupply to position control 116 a binary signal indicative of the width Wof the slab 40a to be pushed.

. As described above, the traverse motors 92 drive a shaft 69 to imparta rectilinear motion to the extractors 62. More specifically, theextractors 62 are driven to the left as shown in FIG. 1 into the furnace32 and then after being lifted upon the platform 76 are withdrawn agiven distance dependent upon the width W of the slab 40a to bedeposited upon the furnace delivery table 50. The computer 114 may serveto initiate the forward stroke of the extractor 62 and also thewithdrawal of the slab 40a upon the extractor assembly 60. A signal maybe supplied by the computer 114 to a position regulator 128 to initiatethe operation of the motors 92 and to provide an indication of the widthW of the slab 40 to be withdrawn. In turn, the position regulator 128applies an operating signal to a traverse regulator 130, which in turncontrols the potential applied by a power supply 132 to the traversemotors 92. It is understood that the traverse motors 92 may be of thevariable voltage type, whose speed is dependent upon the potentialsupplied thereto by the power supply 132. In the alternative, thetraverse regulator 130 and the power supply 132 could be replaced by aconstant voltage source with contactors controlled by the positionregulator 128.

The speed detectors 96, which are connected to the traverse motors 92,generate and apply output signals indicative of the speed of theextractors 62 to the traverse regulator 130. The feedback control loopformed by the speed detectors 96 ensure that the slabs 40 are withdrawnat the correct speed. In addition, the position sensors 98, which areconnected as shown in FIG. 3 to the motors 92, provide an output signalwhich is indicative of the position of the extractors 62. The positionindicating signal is fed back to the position regulator 128, whichcompares the position indicating signal derived from the positionsensors 98 with the slab width signal derived from the computer 114 togenerate a difference or error signal for accurately positioning theslabs 40 upon the furnace delivery table 50. In addition, a manualcontrol 131 may be provided to allow the operator to manually positionthe extractors 62. Further, a semi-auto control 129 may be provided toreplace the slab-width signal derived from the computer 114. Morespecifically, the semi-auto control 129 may take the form of a decadeswitch to provide a binary signal indicative of the width of the slabsto be placed on the furnace delivery table 50.

Further, the position regulator 128 serves to initiate the operation ofthe lift motors 88. The lift motors 88 are mechanicaly connected asshown in FIGS. 1 and 3 to the driving members 80 which in turn areconnected to lift the platforms 76. As shown in FIG. 1, when the leadingedge of the extractor fingers 70 approach the index line 44, the maximumstroke of the extractor 62 has been reached. At this point, the positionregulator 128 in response to the position signals derived from the limitswitch 75 (or the position sensor 98) initiates the lift motors 88. Morespecifically, the position regulator 128 applies an appropriateoperation signal to a raise and lower initiate control circuit 134. Thecontrol circuit 134 in turn applies a control signal to a constantvoltage controller 136 which applies an appropriate constant voltage tothe lift motors 88. Illustratively, the lift motors 88 may be constantvoltage motors, whose operation is controlled by the constant voltagecontroller 136. As more specifically shown in FIG. 3, the limit switches90 are connected to the motors 88 to provide an indication of when thelift platform 76 is in its up position. When the up position is reached,the limit switch 90 provides a feedback signal to the constant voltagecontroller 136 to stop the operation of the lift motors 88. As the liftplatform 76 is raised, the extractor fingers 70 are raised up throughthe skids 36 to lift the slab 40a from the skids 36. At this point, thelift motors 88 are stopped, and the extractor assembly 60 Withdrawn.

In order to insert the extractor fingers 70 within the furnace 32, theextractor doors 48 and the furnace doors 46 must be lifted atapproximately the same point in time that the pusher assembly 18 isactivated to push the line of slabs 40a to 4011 into and through thefurnace 32 and that the extractor assembly 60 begins to insert theextractors 60 into the furnace 32. More specifically, an initiate signalis applied to a constant voltage controller 140 which applies anappropriate voltage to the motor 100. As shown in FIG. 4, the motor 100rotates the shaft 104, which in turn lifts the doors 46 and 48. As shownin FIG. 5, a manual control 142 allows the operator to manually lift thedoors 46 and 48. The limit switch 106 is connected to the shaft 104 andwhen the doors 46 and 48 have reached their up position, the limitswitch 106 applies a feedback control signal to the constant voltagecontroller 140 to stop the door motor 100. Further, it is noted thelimit switch 106 provides an interlock with the position regulator 128to prevent the extractor assembly 60 from being driven to the left asshown in FIG. 1 by the traverse motors 92 when the doors 48 and 46 arein their down position.

In preparation to operating the furnace delivery and exit system 10 inan automatic mode, a plurality of slabs 40 are brought one at a time tothe furnace charging table 14 and pushed into the furnace 32 until thefurnace has been filled. Additional slabs 40 will be pushed into thefurnace 32 until the first or leading slab 40a is brought to theposition where its leading edge. coincides with the index line 44. Asshown in FIG. 1, a detector 42, which may take the form of a televisioncamera, allows the operator to manually position the line of slabs sothat the leading edge of the slab 40a to be discharged is on the indexline 44. It is noted that an auto-initiate control circuit 144 is a partof the control system 112 and may illustratively include a suitableclock mechanism for initiating the various processes of the system atdesired times. In addition, the auto-initiate circuit 144 allows theoperator to begin the process whereby the slab 40 is taken from thefurnace delivery table 12 and placed into the furnace 32, while theextractor assembly 60 is extracting a slab from the furnace 32 andplacing it on the furnace delivery table 50.

After the leading edge of the slab 40a has been disposed on the indexline 44, the operator manually brings the pushers 20 until its teeth 26abut the trailing edge of the slab 4011. Then the operator eitherthrough the autoinitiate circuit 144 or the computer 114 causes thecomputer 114 to interrogate the position sensor 39, through the positioncontroller 116, to determine the encoder position of the shaft 22 andtherefore the pushers 20. The computer 114 will then command the pushermotors 24 to retract the pushers 20 to their full retract position, i.e.the position shown in FIG. 1. As the pushers 20 approach their fullretract position, the limit switch 41 will provide a feedback signal tothe position control 116 to thereby stop the pusher motors 24. Thecomputer 114 will again interrogate the position sensor 39 to determineits encoder position with the pushers 20 in their retracted position.Knowing the two encoder positions of the sensor 39, the computer 114will then know the open skid space available. The open skid space isthat space between the edge of the furnace charging table 14 and thetrailing edge of the slab n. The pushers 20 will remain in the retractposition until the computer 114 gives it the :ommand to go forward topark or to push the slabs 40.

Due to the fact that the slab width is constantly changing in randompattern, there will be many cases when more than one slab must becharged for each slab delivered. In other case, multiple slabs will haveto be delivered for each slab to be charged. For this reason, when thefurnace delivery and exit system 10 is being operated in the automaticmode, the computer 114 will determine after each charging round whetheror not there is sufficient room to park another round of slabs beforepushing. In other words, it is desired to keep the skids 36 as full aspossible at all times without blocking the furnace charging table 12.When a slab 40 has been brought to the furnace charging table 12 and hasbeen parked, the pushers 20 will remain across the furnace chargingtable 12 to wait for the signal to push the first slab 40a to theextractor position 45. Other slabs 40 may now pass under the pushers 20to the other furnaces. Next, the computer 114 interrogates the positionsensor 39 to determine, the distance the pushers 20 may advance theslabs 40 in the furnace 32, which distance is denoted by the leiter X inFIG. 1. As explained above, the width of each of the slabs 40 in thefurnace is stored within the memory of the computer 114. In preparationto pushing the slabs 40, the computer 114 determines whether thedistance X is equal to or greater than the Width W of the slab 40a to bedelivered. If the dimension X is greater than W the control system 112is prepared to push the series of slabs 40 through the furnace 32 tothereby place slab 40 in the extractor position 45. It is understoodthat the time of delivery to the delivery furnace table may bedetermined by the schedule of the finishing and roughing mills, and thatthe same computer 114 may serve to control the functions of thefinishing and roughing mills. Thus, when an additional slab is neededfor the mills, the computer 114 will initiate the pushing operation andas will be explained, the sequencing of the extractor assembly and thelift assembly 74. If the computer 114 determines after the slab 40 hasbeen parked, that the dimension X is less than the width W of the slab40a, the computer 114 will not allow the pushing cycle to be commenceduntil another slab 40 has been parked upon the skids 36.

When the slabs directed to the next furnace have been cleared of thefurnace charging table 12, and the next slab is brought up to thefurnace charging table preceding table 12, one of two conditions mayexist. First, the furnace 32 may have already pushed slab 40a to theextractor position 45 and have withdrawn the pusher 20 to the retractedposition. In this case, the new slab will come to rest upon the furnacecharging table 12 and be pushed onto the skids 36. However, the slab 40amay not have been delivered to the extractor position 45 since the lastslab 40 was placed upon the skids 36. In this case, the computer 114interrogates the position sensor 39 to determine whether the distance Xis equal to or greater than the slab width W of the slab 40a to bepushed to the extractor position 45. If as determined by the computer114 the dimension X is not equal to or greater than the width W thepushers 20 are retracted and the new slab 40 will be. positioned uponthe furnace charging table 12, to be pushed upon the skids 36. Ifhowever, the dimension X is equal to or greater than the width W of theslab 40a to be delivered, the computer 114 must look to see how muchtime remains before the slab 40a is to be extracted from the furnace 32.The extractor assembly 60 requires a certain amount of time to extractthe slab 40a and to place it upon the furnace delivery table 50. If thetime before the next slab 40a is to be delivered is equal to or greaterthan the required delivery time, i.e. in the order of 30 seconds, asdetermined by a clock mechanism within the computer 114, the pushers 20will be withdrawn, and the new slab will be positioned upon the furnacecharging table 12 and pushed upon the skids 36. It is particularly notedthat the dimension X is updated by the computer 114 each time a slab isto be pushed. It is noted that there is a limit to the aggregate widthof slabs that may be disposed upon the skids 36. The slabs 40 may becontinued to be parked upon the skids 36 and until the trailing edge ofthe last slab to be parked interferes with the travel of the slabs downthe furnace charging tables. In order to prevent the dimension X fromincreasing to the point where the furnace charging table 20 will beblocked, the computer must insure that the pusher assembly 18 isoperated in order to remove the slab 40a or in the alternative, to stopthe oncoming slabs on the furnace charging table preceding table '12.

Any random difference in the total width of the slabs in one furnacewith respect to the other furnaces, may cause trouble which may be takencare of by the insertion of a dummy slab.

During the operation of this system in an automatic mode, the operatorshould occasionally check the position of the leading edge of the slab40a to be delivered with respect to the index line 44. When the operatordiscovers that the index line 44 is drifting with respect to the leadingedge of slab 40a, the operator should manually advance the pusher 20 tocorrectly position the leading edge of the slab 40a with respect to theindex line 44 and then to manipulate the computer to recalibrate theclear space as explained above.

In preparation to operating the extractor assembly 60, the extractors 62are driven to their maximum extended position in which the extractorfingers 70- are disposed to lift the slab 40a to be delivered, and thecomputer 114 interrogates the position sensor 98 (through the positionregulator 128) to determine the encoder position of the fully extendedextractor assembly 60. When the furnace delivery table 50 is ready toreceive the next slab from the furnace 32, an initiate signal is derivedeither from the auto initiate control 144 or the computer 114 to startthe pushing cycle of the pusher assembly 18. When the pushers 20 havebeen extended a distance sufficient to push the series of slabs adistance corresponding to the width W of the slab 40a to be extracted, afeedback signal is developed by the position sensor 39 and applied tothe position regulator 128. The position regulator 128 compares thefeedback signal with the input signal derived from the computer 114 andindicative of the width W to generate an error signal. When the errorsignal equals zero, the position control 128 will stop the operation ofthe pushers 20. Now, the slab 40 will have been disposed in the extractposition 45 and the slab 4012 will be repositioned so that its leadingedge coincides upon the index line 44.

At the same time, the pushing cycle is commenced an initiate signal isgiven to the extractor assembly 60- to start an extracting cycle andalso to the constant voltage control 140 to raise the extractor doors4'8 and the furnace exit doors 46. When the doors 46 and 48 have beenlifted to their up position, the limit switch 106 applies a feedbacksignal to the consent voltage controller 140- to stop the operation ofthe motor 104. At the same time the doors 46 and 4-8 are being raised,the position regulator 128 initiates the operation of the traversemotors 92 to drive the extractors 62 toward and into the furnace 32. Asnoted in FIG. 1, the height of the extractor fingers 70 during theinitial thrust is below the height of the rollers 52, so that thefingers 70 will not interfere With the slab in the extract position asthe extractor moves into the furnace. When the extractors 62 are fullyextended Within the furnace 32, the limit switch 75 provides a feedbacksignal to the position regulator 128, which causes the motors 92 tostop. It is noted that a similar signal could be developed by theposition sensor 98. In addition to stopping the motors 92, the positionregulator 128 provides an initiate signal to the automatic raising andlowering initiate control 134, which in turn starts the lift motors 88to raise the life platform 76. As the lift platform 76 is driven upward,the extractor fingers 70 contact and lift the slab 40 from the skids 36.When the lift platform 76 has reached its upper position, the limitswitch 90 will provide a feedback signal to the constant voltagecontroller 136 to stop the lift motors 88 and also to the positionregulator 128 to initiate the withdrawal of the extractor 62.

With reference to FIG. 1, it is desired to place slab 40a upon thefurnace delivery table 50 so that the centerline of the slab 40acoincides approximately with a centerline 51 of the furnace deliverytable 50. As explained above, the width of each of the slabs 40 in thefurnace 32 are stored in the memory section of the computer 114. As theslab 40a is being withdrawn by the extractor 60, a position signal isgenerated by the position sensor 98 and applied to the positionregulator 128, which compares this position signal .with a signaldeveloped by the computer 114 indicative of the desired placement of theslab 40a upon the furnace delivery table 50. The slab 40a is withdrawnupon the extractor 62 a distance equal to the spacing between the indexline 44 and the centerline 51 minus /2 the width W of slab 4021. Whenthe error signal developed within the position regulator 128 equalsapproximately zero, the position regulator 128 causes the traversemotors 92 and the extractor assembly 60 to stop and then applies alowering initiate signal to the control 134. In turn, the automaticraise and lower initiate control 134 starts the lift motors 88 totherefore lower the lift platform 76. When the lift assembly 76 reachesits lower position, the limit switch 90 provides a feedback signal tothe controller 136 to stop the lift motors 88. At this point with thelift platform 76 in its lowered position, the slab 40a has been disposedupon the furnace delivery table 50 within its centerline coinciding withthe centerline 51 of the table 50. It is noted that the limit switch 90connected to the lift motors 88 may also provide an interlock to themotor 58 driving the furnace delivery table 50. Thus when the liftassembly 76 is in an up position, the motor 58 is prevented fromoperating and when the lift platform 76 is down, the motor 58 is allowedto drive the rollers 52 of the table 50*.

When the double row slabs are being extracted, they will be pushedtogether, but will be extracted one at a time by the extractor assembly60. The computer 114 may be used to control the magnetic clutch tooperate the extractors 62 separately.

The furnace delivery system 10 may also be operated in thesemi-automatic mode. As in the automatic operation, the pushers 20 andthe extractors 62 are calibrated in their extended and retractedpositions. Instead of relying upon the computer 114, the operator wouldnote the encoder signals from the position sensors 39 and 98. First, aslab 40 would be delivered to the furnace delivery table 12 and would bepositioned either manually or automatically. Then the operator manuallyoperates the pushers 20 to slide the slab 40, upon the skids 36 so thatit is in contact with the slabs 40 already on the skids 36. Next, theoperator takes a look at a display derived from the camera 42 to checkthat the leading edge of the slab 40a to be discharged is disposed uponthe index line 44. The pushers 20 are now left in this position, whilethe operator determines the width W of the slab 40a to be extracted andsets the width W into the semi-automatic controls and 129. As explainedabove, the controls 120 and 129 may include decade switches into whichmay be set accurately the width W of the slab 40a. When it is desired toextract the slab 40a, the operator will initiate simultaneously throughthe semi-auto controls 120, 129, a push cycle and a retract cycle. Uponthe actuation of these controls, the furnace exit extractor doors 46 and48 will be drawn upward by the motor 100 until the limit switch 106applies a feedback signal to the control 140 to stop the motor 100. Atthe same time, the extractors 60 are driven into the furnace 32 untilthe limit switch 75 causes the traverse motors 92 to stop. At the sametime, the pushers 20 are driven forward by the pusher motors 24 adistance W corresponding to the width of the slab 40a to be extracted.As the pushers 20 complete their stroke, the position sensor 39 providesa feedback signal to the position control 116, which compares thisfeedback signal with the input signal derived from the control 120 toprovide an error signal which will be fed to the position regulator 128.When a zero error signal is obtained from the position control 116 and afeedback signal is derived from the limit switch 106 indicating that thedoors 46 and 48 are in a raised position, the position regulator 128will initiate through the control 113, the raising of the lift platform76 and therefore the extractor 62. At the same time the position control116 derives a zero error signal, the position control 116 will alsoretract the pushers 20. When the lift platform 76 is raised and thefurnace exit doors 46 are open, the extractors 62 will be withdrawn fromthe furnace 32 to position the slab 40a on the centerline 51 of thefurnace delivery table 50. The extractors 62 will be withdrawn adistance equal to the spacing between the index line 44 and a centerline51 minus /2 the width W of the slab 40. The positioning of the extractor62 will be controlled by the position control 129, which compares thefeedback signal derived from the position sensor 98 with a referencesignal derived from the control 129. The furnace exit doors 46 will beclosed when the extractors 62 have cleared the door 46. Finally, thetextractor 62 will lower the slab 40 onto the furnace delivery table 50.At this point, both the extractors 62 and the pushers 20 will be inposition for the next cycle when the operator desires to initiate it.

Since numerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof it is intended that all matter contained in theforegoing description are shown and the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A system for controlling the movement of slabs relative to a furnaceincluding first support means for receiving at least one of said slabs,first displacement means for delivering at least one said slab from saidfirst support means into said furnace, second displacement means forextracting at least said one slab from said furnace, second supportmeans upon which said second displacement means deposits at least saidone slab, and control means into which at least one dimension of atleast said one slab may be set to determine the displacement imparted toat least said one slab by both said first and second displacement means.

2. A control system as claimed in claim 1, wherein there is includedfirst detecting means for sensing the displacement imparted to at leastsaid one slab by first displacement means, and second detecting meansfor sensing the displacement imparted to at least said one slab by saidsecond displacement means.

3. A control system as claimed in claim 2, wherein said first and seconddetecting means develop respectively first and second output signalsindicative of the displacements imparted to at least said one slab byfirst and second displacement means, said control means comparing saidfirst and second output signals with said one dimension to therebydetermine the displacement imparted to at least said one slab by both ofsaid first and second displacement means.

4. A control system as claimed in claim 3, wherein said control meansincludes a computer having a program storage capability for storing saidone dimension of at least said one slab.

5. A control system as claimed in claim 4, wherein said control meansincludes first and second position controls for controlling the positionrespectively of said first and second displacement means, said computerapplying output signals indicative of said one dimension of said slab tosaid first and second position controls, said first and second detectingmeans applying respectively said first and second output signals to saidfirst and second controls, said first and second position controlscomparing the signals derived from said computer with said first andsecond output signals to thereby control the displacement of at leastsaid one slab.

6. A control system as claimed in claim 1, wherein each of said slabs isdisposed in the line on third support means disposed within saidfurnace, said first displacement means pushing said line of slabs sothat the first slab of said line is disposed in an extract position,said second displacement means including extractor means, extractordrive means suitably connected to said extractor means for disposingextractor means Within said furnace, lift means associated with saidextractor means, and second suitable drive means for lifting said liftmeans and said extractor means to thereby displace each of the slabsdisposed Within said furnace support means.

7. A control system as claimed in claim 6, wherein a first positionsensor is associated with said extractor means for providing a firstoutput signal indicative of the position of said extractor means, and asecond position sensor associated with said lift means for providing asecond output signal indicative of the position of said lift means.

8. A control system as claimed in claim 7, wherein said control meansincludes position control means for controlling the operation of saidextractor drive means, said first position sensor applying said firstoutput signal to said position control means, said position controlmeans comparing said first output signal with said one dimension of theslab to be disposed in said extract position to control the displacementimparted by said extractor means to the slab to be extracted so that theslab to be extracted is disposed upon said second support means.

9. A control system as claimed in claim 8 wherein said second positionsensor provides that said second output signal indicates that saidextractor means is in an extended position and applies said secondoutput signal to said position control means, said position controlmeans initiating the operation of said lift drive means to raise saidlift means.

10. A control system as defined in claim 6, wherein there is included atleast one door through which said extractor means is disposed into saidfurnace, and door drive means associated with said door to selectivelyraise and lower said door.

11. A control system as claimed in claim 10, wherein said control meanssimultaneously initiates the pushing of said line of said slabs, themovement of said extractor means into said furnace, and the opening ofsaid door.

References Cited UNITED STATES PATENTS 2,397,339 3/1946 Crosby 2l4-233,407,944 10/1968 Gustashaw et al. 21426 ROBERT G. SHERIDAN, PrimaryExaminer

